It is known that compressed natural gas can be transported on a vessel equipped with tanks formed as cylinders, which tanks are prepared from special steel. Also known are vessels for transport of compressed natural gas, comprising tanks in the form of high-pressure steel pipes, arranged either along the longitudinal axis of the vessel or as coils on-board the vessel. For vessels having tanks prepared from steel it can however be a significant problem that the load constitutes a relatively small part of the total weight of the vessel, which means a high cost of transportation. It is known that use of composite tanks can be preferable, because of possibility for significantly reduced weight of the tanks per se. A composite tank can preferably be prepared by starting with a high-density polyethylene (HDPE) diffusion barrier innermost in the tank, outside which diffusion barrier an adhesive impregnated glass- or carbon fibre winding is arranged to increase strength. The windings are made in a spiral pattern with pre-tensioning of the fibers. The end sections of such a tank is typically prepared with an integrated boss of alloyed steel, to which feed-throughs are welded or bolted.
In Patent Publication U.S. Pat. No. 6,339,996 B1 it is described that comparable composite pressure tanks can result in a weight saving of up to 70% relative to steel tanks. In said patent publication, a vessel having such composite tanks is described. The tanks are arranged vertically aligned in the vessel, the tanks being arranged vertically standing in three heights inside the hull of the vessel. This results, however, in stability problems if the upper layer of tanks contains significant quantities of liquid, while the lower layer of tanks mainly contains gas. Therefore, a complex system of manifolds, lines, valves and connections, is arranged in said vessel. The tanks and the comprehensive pipe system according to said publication are arranged in a closed space inside the vessel. Repair or replacement of damaged tanks or components within the closed space is very laborious and expensive.
A demand exists for a vessel for transport of compressed natural gas or combination of gas and liquid, which vessel is preferable relative to the above-mentioned problems.